Brand Registration and Selling

Hi Everyone ! I am fairly new to selling on Amazon. I have applied for the trademark for my brand here in the UK. I have not applied for the trademark in the US. I tried getting my brand registry done on Amazon and it got rejected.

My question is. Can I move forward to sell in the UK and in the US without while I wait for the brand registration, or do I wait for the registration to be done and only then I can start selling.

This is all for FBA

Thanks
Lyndon